1. Field of the Invention
The present invention relates to a mounting substrate and a structure having a semiconductor element mounted on the substrate and, more particularly, to a mounting substrate for mounting thereon a semiconductor element having a line of electrode terminals and a structure having a semiconductor element mounted on the substrate.
2. Description of the Related Art
A structure, in which a semiconductor element is mounted on a substrate by flip chip bonding, the semiconductor element comprising a plurality of electrode terminals arranged in two rows at the central portion of the surface thereof, is known. FIG. 12 shows a method of mounting a semiconductor element 10 on a substrate 20 to provide such a structure. Electrode terminals (not shown) of the semiconductor element 10 are each provided with a protruded electrode 12 of a gold bump, and connection electrodes 22 are arranged, corresponding to the protruded electrodes 12, on the surface of the substrate 20 on which the semiconductor element 10 is to be mounted. The connection electrodes 22 and the protruded electrodes 12 are aligned with each other, and the semiconductor element 10 is mounted on the substrate 20. The surface of the connection electrodes 22 is deposited with solder (not shown). The semiconductor element 10 is heated to a temperature at which the solder is melted, and the protruded electrodes 12 are bonded under pressure to the connection electrodes 22.
FIG. 13 is a sectional view showing a structure in which the semiconductor element 10 is mounted on the substrate 20. The connection electrodes 22 arranged on the surface of the substrate 20 where the semiconductor element is to be mounted include solder deposited on the surface of a copper pattern 23.
The protruded electrodes 12 of the semiconductor element 10 are arranged in two rows. The connection electrodes 22 are also arranged in two rows on the substrate 20 at positions corresponding to the protruded electrodes 12. The connection electrodes 22 are exposed from the protective film 32, such as a solder mask, covering the surface of the substrate 20 on which the semiconductor element is to be mounted. Actually, as shown in FIG. 12, the area of the surface of the substrate 20, in which the semiconductor element 10 is to be mounted and the connection electrodes 22 are arranged, constitutes an exposed rectangular opening 30. The solder 24 on the connection electrodes 22 is exposed in the opening 30, while the portion other than the opening 30 is covered with a protective film 32, such as a solder mask, as shown in FIG. 13. The connection electrodes 22 are each connected with a wiring pattern 26, which in turn is covered by the protective film 32.
Apart from the structure as shown in FIG. 12 in which the semiconductor element having protruded electrodes arranged in two rows is mounted by flip-chip bonding, there is a structure in which a product, such as a memory chip, having a plurality of protruded electrodes arranged in a single row substantially along the center line of the product is mounted. In the structure in which a product having the protruded electrodes arranged in a single row is mounted on a substrate, the connection electrodes of the substrate are also arranged in a single row at positions corresponding to the protruded electrodes.
In the case where a semiconductor element with protruded electrodes arranged in one row is mounted as described above, the problem described below is posed.
FIG. 14A shows the substrate 20 aligned with the semiconductor element 10 having a protruded electrode 12. FIG. 14B shows the state in which the protruded electrode 12 is brought into contact with the connection electrode 22 of the substrate 20 and heated under pressure to thereby bring the end surface of the protruded electrode 12 into contact with the surface of the connection electrode 22. As the result of the protruded electrode 12 coming into contact with the connection electrode 22, the connection electrode 22 and the substrate 20 are partially depressed. FIG. 14C shows the state in which the temperature is decreased until the solder 24 on the connection electrode 22 is solidified to thereby release the pressure imparted on the protruded electrode 12.
Once the solder 24 is solidified and the pressure is released from the protruded electrode 12, as shown in FIG. 14C, the semiconductor element 10 comes to be mounted at an angle to the surface of the substrate 20 by the elasticity of the substrate 20 and the connection electrode 22. This is by reason of the fact that, in the case where the protruded electrodes 12 are arranged in two rows as shown in FIG. 13, the distortion imparted on the semiconductor element 10 is distributed equally between the right and left sides in the drawing, whereas in the case where the protruded electrodes 12 are aligned in one row as shown in FIG. 14C, the stress on the semiconductor element 10 loses balance and more strongly acts on one side.
In the case where the semiconductor element 10 is mounted obliquely on the substrate 20 as shown in FIG. 14C, the reliability of electrical connection between the protruded electrodes 12 and the connection electrodes 22 is deteriorated, or the underfill material 34 (FIG. 13C) fails to be sufficiently filled up between the semiconductor element 10 and the substrate 20, thereby forming a void. This derives from the fact that when the semiconductor element 10 is mounted at an angle, the interval between the semiconductor element 10 and the substrate 20 is partially reduced to less than that required to allow the underfill material 34 to be adequately filled therein.
In the case where underfill material is filled after bonding the semiconductor element 10 to the substrate 20, care must be taken not to generate any void in the sealed area. A resin material having a high fluidity is used as the underfill material 34. Nevertheless, it is very difficult for the underfill material to flow sufficiently in the very narrow space between the semiconductor element 10 and the substrate 20. Especially in the region where the protruded electrodes 12 and the connection electrodes 22 are connected with each other and where the underfill material 34 does not easily flow, a void is liable to occur.
The present invention has been achieved to obviate the aforementioned problems, and an object of the invention is to provide a highly reliable mounting substrate and a structure in which a semiconductor element having protruded electrodes arranged in a line substantially along the center line of a surface of the semiconductor element is mounted on a substrate by flip-chip bonding in such a manner that the protruded electrodes of the semiconductor element and the connection electrodes of the substrate are securely connected electrically to each other, with the underfill material being sufficiently filled in the space between the semiconductor element and the substrate.
According to one aspect of this invention, there is provided a mounting substrate, on which a semiconductor element is to be mounted by flip chip bonding, the semiconductor element having a surface on which a plurality of electrode terminals are formed so as to be arranged in a line, each of the electrode terminals having a protruded electrode formed thereon,
wherein the surface of the mounting substrate on which the semiconductor element is to be mounted is provided with a protective film having an opening corresponding to an area of the semiconductor element where the protruded electrodes are located, a plurality of connection electrodes being arranged in the opening, the connection electrodes being provided with a solder for bonding it to the protruded electrodes, and being arranged at the same interval as that of the protruded electrodes, and each of the connection electrodes being connected to a wiring pattern of the mounting substrate, and wherein the length of a portion of the connection electrode from the center of the opening to the end thereof that is not connected with the wiring pattern is 150 xcexcm or larger.
The connection electrodes preferably extend from one edge of the opening to a position under the protective film beyond the other edge of the opening.
Preferably, the length of the portion of the connection electrode from the center of the opening to the end thereof that is not connected with the wiring pattern is not less than 200 xcexcm.
The connection electrodes can each have, at the central portion thereof located in the opening, a connection area wider than the wiring pattern, and have, at both sides of the connection area, an extension area of substantially the same width as the wiring pattern.
Preferably, the number of the wiring patterns connected to the connection electrodes from one side of the opening is substantially equal to the number of the wiring patterns connected to the connection electrodes from the other side of the opening.
Preferably, the opening extends outside of the area on which the semiconductor element is to be mounted, in the same direction as the line of the protruded electrodes of the semiconductor element.
It is especially preferable that the opening extends at least 50 xcexcm outside of the area on which the semiconductor element is to be mounted.
According to another aspect of the invention, there is provided a structure in which a semiconductor element is mounted on a substrate by flip chip bonding, the semiconductor element having a surface on which a plurality of electrode terminals are formed so as to be arranged in a line, each of the electrode terminals having a protruded electrode formed thereon, wherein an underfill material is filled in the space between the surface of the semiconductor element provided with the electrode terminals and the substrate, and wherein the substrate is a mounting substrate of the invention as described above.